The present invention relates to a hydraulic idling-regulating valve means for controlling movements of a machine element drivable by a hydraulic cylinder. The valve means includes at least two mechanically operated through-flow valves arranged in a casing and controlled, by the reciprocating movements of an actuating element, to move from a neutral central position with both valves closed into alternative directions into a flow position and closure position. An electromechanical specified-value setting system and a mechanical actual-value feedback system are provided for setting and/or controlling the specified and actual values of the instantaneous position of the pistons of the driving hydraulic cylinder. The specified-value setting system comprises a hollow shaft rotatably mounted in a housing of the valve means and reciprocable in the longitudinal direction. The hollow shaft rotates a number of revolutions correlated with the respective specified value, by electric motor provided for the purpose of controlling the specified value. The actual-value feedback device comprises a feedback spindle engageable, via an external thread, with an internal thread of the hollow shaft and which is coupled, by form-locking means, to move with a piston of the driving hydraulic cylinder either, when the connection with the piston is rigid, in such a manner that it follows any displacement of the latter or, in the case of a rotational connection with the piston, in such a manner that it performs a number of rotations correlated with the movements of the piston, in which case the valve-actuating member is subjected to the same displacements in the axial direction as the specified-value setting shaft, with the specified-value setting shaft being rotatably supported in the valve-actuating element which in turn is secured against rotation in the casing.
Idling-regulating valves of the aforementioned type have been proposed in DE-PS 20 62 134 and DE-OS 29 10 530, and are equipped with an electromechanical specified-value setting system and a mechanical actual-value feedback system for setting and/or controlling the specified and actual values of the instantaneous position of the pistons of the driving hydraulic cylinder. The specified-value setting system, which comprises a hollow shaft mounted to rotate in the housing of the valve and to reciprocate in the longitudinal direction, is rotatable a number of revolutions correlated with the respective specified value, by an electric motor provided for the purpose of controlling the specified value. The actual-value feedback system comprises a feedback spindle which, is in engagement via an external thread with an internal thread of the hollow shaft and which is movably coupled in a form-locking manner with the piston of the driving hydraulic cylinder either, when the connection with the piston is rigid, in such a manner that it follows any displacement of the latter or, in the case of a rotational connection with the piston, in such a manner that it performs a number of rotations correlated with the movements of the piston, in which case the valve-actuating member is subjected to the same displacements in the axial direction as the specified-value setting shaft, the latter being rotatably supported in the valve-actuating element which in turn is, however, secured against rotation in the casing. The casing in which the pressure tank and supply ducts leading to the individual through-flow valves as well as the consumer connection ducts leading from the valves to the controlled hydraulic cylinder are integrated, have been implemented heretofore as aluminium die-castings comprising the valve cores and bores accommodating the specified-value setting hollow shaft and the actual-value feedback spindle as well as the space for the valve-actuating element which can be described as being arranged between the valve cores and actuating the latter by a radially projecting actuating element.
However, a particular disadvantage of conventional idling-regulating valves resides in the complex structure of the casing which requires considerable space and which necessitates a very complex and expensive core for casting. In addition, the aluminium casing must be very solid if the required tightness is to be ensured against the highly pressurized working medium, i.e., a pressure fluid, with the working pressures reaching 200 bar. Accordingly, high demands must be placed upon the quality of the cast housing and it is not rare that it is found only during the final production test of the finished idling-regulating valve that the casing is porous and has, therefore, to be rejected, a process which is of course connected with additional costs.
Now, it is the object of the present invention to provide an idling-regulating valve of the type described above which can be realized with considerably smaller outer dimensions and can be produced much more easily and rationally from steel, without any sacrifices as to control accuracy and operating reliability.
This object is achieved according to the invention by an arrangement characterized in that the casing has a circular cylindrical core with at least one first longitudinal bore in which are arranged longitudinally movable pistons of a pair of valves, between stop elements which are fixed against rotation relative to the casing, but mobile in the longitudinal direction. Another bore is provided in which the hollow shaft of the specified-value setting system, which can be driven by the electric motor, is mounted in a rotatable and longitudinally movable manner. The stop elements are carried axially and radially on the specified-value setting shaft via pivot pads. The casing is further provided with a cylindrical circular envelope into which the core is firmly set, with the connection spaces on the pressure-source side and the consumer side which, depending on the position of the valve pistons are either connected to communicate with each other or closed against each other, being defined by external grooves on the cylindrical core and by inner surface areas of the envelope fixed thereto, and inlet and outlet ducts being defined by radial bores in the core and the envelope.
This solution is advantageous in that the arrangement of the stop elements of the valve-actuating element outside the valve bores reduces the required space in the radial direction so that the space required for the idling-regulating valve as a whole is notably reduced. The circular cylindrical design of the core of the valve casing and its outer envelope enables these parts to be implemented as machined steel parts which can be produced by simple operations on usual machine tools, at high precision.
It can be fitted into the bore of a machine part having a diameter corresponding to the outer diameter of the envelope of the casing, in which case the supply and consumer connections are to be provided in the housing part of the machine.
The idling-regulating valve according to the invention is suited not only for controlling linear drives, but also for controlling rotary drives designed to perform a plurality of rotations in a given sense of rotation, as well as for controlling pivot drives with limited pivot angle. When used for controlling rotary drives, particular advantages are offered by a construction; of the regulating valve where a feedback system comprises a feedback spindle which is fixed on the driven rotary or pivoting part to rotate therewith.
This last-mentioned embodiment of the idling-regulating valve according to the invention is particularly well suited for controlling hydraulic pivot drives of multi-joint industrial robots where the idling-regulating valve can be accommodated without any difficulty in the universal-joint shaft.
According to another object of the invention, the firm connection between the core and the envelope of the casing is achieved by thermal shrinking of the envelope and/or thermal expansion of the core, after the latter has been cooled down.
Another embodiment of the invention provides that, prior to being shrunk upon the core, the envelope is heated up to a temperature of 400.degree. K., and the core is cooled down in liquid air or liquid oxygen to a temperature of substantially 150.degree. K., preferably, by 80.degree. K.
According to a further embodiment of the invention, the specified-value setting shaft and the bore accommodating the feedback spindle extend along the central longitudinal axis of the idling-regulating valve and at least two bores accommodating the pistons of one pair of valves each are provided in rotary symmetrical relationship relative to the central longitudinal axis.
According to still another embodiment of the invention, the envelope is provided with external annular grooves delimiting separate envelope portions, with the radial supply and consumer connection ducts ending each in one of the envelope portions, and the valve casing embracing the core and the envelope can be accommodated in a bore of an outer housing block in which separate sections are sealed against each other by sealing rings, with ducts run in the outer housing block and corresponding to the supply and consumer connections of the envelope opening into the said bore sections.
Still another embodiment of the invention provides that the pistons of each of the pairs of through-flow valves accommodated in one of the longitudinal bores of the core are supported against each other by a biased spring and the stop elements are provided with control elements for setting the positions of the valve pistons between the stop elements.
According to another embodiment of the invention, the feedback spindle is fixed to the rotary part of the pivot drive so as to rotate therewith.
Finally, one embodiment of the invention provides that it is used in drives for the joints of multi-joint robot arms.
Other details and features of the present invention will become apparent from the following description of several embodiments of the invention with reference to the accompanying drawings.